1. Field of the Invention
The present invention relates to techniques for improving the throughput and reliability of optical fiber links by coherently bonding multiple communication channels together. More particularly, the invention relates to techniques for using multiple orthogonal wavefronts propagating concurrently through multiple optical paths in a fiber to provide enhanced communications via increased channel bandwidth. Furthermore, the same techniques can be modified to enhance amplified signal power thus increasing the effective communications range of the optical data communications
2. Description of Related Art
It is well known in the art that increasing the bandwidth and reliability of a communication interface can be achieved by combining, or bonding, two or more sets of interface hardware. An electro-optical (E/O) network interface card on a host processor, for example, may be limited to a certain maximum data rate over an optical fiber. A second E/O network interface card can be added to the host processor, and software running on the host processor can be made to divide up information packets across the two E/O network interface cards such that portions of a message to be transmitted are sent over both E/O network interface cards simultaneously. If each network card operates at its full bandwidth, the combined bandwidth of the entire optical fiber system is effectively doubled. At the receiving end, the two network data streams are received simultaneously, and the receiving processor reassembles the transmitted data message by properly organizing the packets received from each of the two network interface cards.
The channel bonding methods described above are generally applied to hard-wired connections over copper wire or fiber optics because such hard-wired systems provide good isolation between the two or more independent communication channels. Assuming there is a customer need to deliver two signal streams from a source location to a destination through a fiber network. The capacity of a single fiber channel is adequate enough only to have one signal stream delivered, but not wide enough to have both signals streams delivered concurrently. Channel bonding technique combining two optical channels will enable the customer to deliver both signal streams to the destination concurrently. Let us denote the two available optical channels as Channel 1 and Channel 2. The two optical channels feature active optical sources connecting a source location (S) and the destination (D). The two signal streams are denoted as A and B. Conventional channel bonding will use
Channel 1 for signal stream A, and
Channel 2 for signal B.
On the other hand, WF muxing will enable two signals streams A and B propagating through the two channels, Channel 1 and Channel 2, more efficiently. WF muxing techniques will use Channel 1 for a linear combination of the signal stream A and the signal stream B while use Channel 2 for a second linear combination of the signal stream A and the signal stream B. Let us choose a set of combinations such that
Channel 1 for a signal stream A+B, represented as S1, and
Channel 2 for a signal stream A−B, denoted as S2.
The distribution of the “weightings” of signal stream A between Channels 1 and 2 is represented as a wavefront (WF) vector [1, 1]. Similarly, the distribution of the “weightings” of signal stream B between Channels 1 and 2 is represented as another WF vector [1, −1]. These two WF vectors are mutually orthogonal to one another. However, signal stream A and signal stream B are completely independent. As long as the two propagation channels, Channels 1 and 2, are equalized, the two signal streams will remain orthogonal when arrive at a destination. Thus the signal stream A and the signal stream B can be reconstituted at the destination viaA=(S1+S2)/2,andB=(S1−S2)/2
The present invention relates to techniques for improving the throughput and reliability of optical fiber links by coherently bonding multiple communication channels together. When coherent bonding is applied to data transmission over an optical fiber, there will be many advantages. One obvious advantage of utilizing WF muxing is dynamic resource allocations.
Two optical fiber channels, Channels 1 and 2, feature two 10 W laser sources to deliver two signal streams A and B. Conventional techniques will independently use Channel 1 for signal stream A and Channel 2 for signal stream B. Therefore, the maximum optical power attributed to the two signal streams is limited to 10 W each. On the other hand when a need is arise to dynamically boost up the optical power associated to signal stream A to 15 W while reduce that to signal stream B to less than 5 W, the present invention will be able to deliver the dynamic optical distribution by adjusting the ratio of the input power levels of signal streams A to B to 3-to-1. As a result, 75% of each laser power will be delegated to signal stream A. Signal stream A will have 7.5 W optical powers from the first laser source and concurrently obtain another 7.5 W optical power from the second laser source. Similarly, signal stream B will draw less than 2.5 W optical powers from the first laser source and concurrently another 2.5 W optical power from the second laser source.
WF muxing and demuxing techniques can be applied to multiple parallel optical paths, such as multiple mode group propagations in multimode fibers (MMF), multiple wavelength division multiplexing in singles mode fibers, or multiple fibers. As long as there are parallel propagation paths and/or banks of parallel optical sources, WF muxing/demuxing techniques will become very helpful.
There are two propagation effects which limits optical fiber transmission distances for both single mode and multi-mode fibers. The first one is pure propagation attenuations; which reduce optical signal to noise ratios as the transmission increased. Higher power lasers will overcome the propagation attentions to increase transmission distance. The second limiting category is the dispersion effects, which distort optical pulse shapes or optical waveforms, causing inter-symbol-interference (ISI).
Optical communication systems are designed to deliver an end-to-end bit error rate (BER) that does not exceed a desired value, such as 10−12. As dispersion increases, a higher ratio of received signal-to-noise ratio (SNR) is needed to achieve the desired BER. The extra SNR may be required to counteract the effects of dispersion. However, increasing laser power does not guarantee better SNR. Adaptive compensations to equalize dispersion caused by propagations differentials appears to be right approaches to increase SNR. There are three different causes for dispersions in fiber optic communications, (1) phase velocity differentials among different spectral components resulting in chromatic dispersion, (2) group velocity differentials over same spectral components concurrently propagating in multi-paths with different transmission modes resulting in modal dispersion, and (3) differences in transmission speed for light components with different polarizations.